This invention relates to pancreatic islet cell antigens that bind with antibodies found in the sera of patients afflicted with insulin-dependent (Type I) diabetes mellitus (IDDM). More particularly, the invention relates to proteins and peptides that bind with islet cell antibodies (ICA) and that are prepared by recombinant DNA (rDNA) or synthetic methods. The invention also concerns cloned DNA encoding such ICA proteins and peptides. The ICA proteins and peptides of the present invention are useful as immunoassay reagents in the presymptomatic diagnosis of IDDM.
The accumulating evidence of cellular and humoral abnormalities associated with IDDM has led to the hypothesis that the disease is an autoimmune disorder. Serum antibodies directed against the insulin-producing beta cells of the pancreatic islets have been detected by immunofluorescence, [G. F. Bottazzo, A. Florin-Christensen, and D. Doniach: Islet Cell Antibodies in Diabetes Mellitus With Autoimmune Polyendocrine Deficiencies, Lancet ii:1279-1283 (1974), and A. C. MacCuish, J. Jordan, C. J. Campbell, L. J. P. Duncan, and W. J. Irvine: Antibodies to Islet-cell in Insulin-dependent Diabetics With Coexistent Autoimmune Disease, Lancet ii:1529-1533 (1974)]. These autoantibodies are observed in 70-80% of newly diagnosed diabetics (NDD), but only in 0.1-1% of normal control subjects [C. H. Brogren and A. Lernmark: Islet Cell Antibodies in Diabetes. Clin. Endocrinol. Metab. 11:409-430 (1982)], and G. F. Bottazzo, R. Pujol-Borrell, and D. Doniach: Humoral and Cellular Immunity in Diabetes Mellitus. Clin. Immunol. Allergy 1:139-159 (1981)]. ICAs have come to be accepted as one predictive factor for IDDM. A review of current knowledge on ICA is provided by A. Lernmark, Diabetic Medicine 4:285-292 (1987).
The conventional ICA assay consists of exposing pancreas sections to sera, staining with a second antibody bearing either a fluorescent [G. F. Bottazzo et al., supra] or enzyme label [P. G. Colman, M. Tatkus, A. Rabizadeh, C. Cahill, and G. S. Eisenbarth: Assay for Islet Cell Antibodies with Rat Pancreas and Peroxidase Protein A. Diabetes Care 11:367-368 (1988)], and observing under a microscope. Another similar method involves a biotin-avidin sandwich and immunofluorescent detection [T. Kobayashi, T. Sugimoto, T. Itoh, K. Kosaka, T. Tanaka, S. Suwa, K. Sato and K. Tsuju: The Prevalence of Islet Cell Antibodies in Japanese Insulin-dependent and Non-insulin-dependent Diabetic Patients Studied by Indirect Immunofluorescence and by a New Method. Diabetes 35:335-340 (1986)]. These methods are time consuming, laborious, difficult to reproduce, and have limited sensitivity. The development of a more convenient immunoassay for ICA would permit widespread testing for epidemiology and correlation with IDDM, and ultimately prediction of the disease with a screening test.
A major limitation of current ICA tests is the limited knowledge and characterization of the islet cell antigens involved. The ICA's may be of low titer or affinity and approachable only with characterized antigens. ICA antigens that are detected by the immunofluorescence test are of special interest; these antigens may include:
(1) islet cell surface moieties [N. K. MacLaren, S. W. Hugng, and J. Fogh: Antibody to Cultured Human Insulinoma Cells in Insulin-dependent Diabetes. Lancet 1:997-1000 (1975), and A. Lernmark, Z. R. Freedman, C. Hofmann, A. H. Rubenstein, D. F. Steiner, R. L. Jackson, R. J. Winter and H. S. Traisman: Islet-cell-surface Antibodies in Juvenile Diabetes Mellitus. N. Engl. J. Med. 299:375-380 (1978)], PA1 (2) insulin [J. P. Palmer, C. M. Asplin, P. Clemons, K. Lyen, O. Tetpati, P. K. Raghu and T. L. Paquette: Insulin Antibodies in Insulin-dependent Diabetics Before Insulin Treatment. Science 222:1337-1339 (1983), and S. Srikanta, A. T. Ricker, D. K. McCulloch, J. S. Soeldner, G. S. Eisenbarth and J. P. Palmer: Autoimmunity to Insulin, Beta Cell Dysfunction, and Development of Insulin-dependent Diabetes Mellitus. Diabetes 35:139-142 (1986)], PA1 (3) a 64,000 dalton (64 kd) islet protein of unknown cellular localization [S. Baekkeskov, J. H. Nielsen, B. Marner, T. Bilde, J. Ludvigsson, and A. Lernmark: Autoantibodies in Newly Diagnosed Diabetic Children Immunoprecipitate Human Pancreatic Islet Cell Proteins. Nature 298:167-169 (1982). Recent evidence indicates that the 64kd protein is glutamic acid decarboxylase (GAD). [S. Baekkeskov, J-H. Aanstoot, S. Christgau, A. Reetz, M. Solimena, M. Cascalho, F. Folli, H. Richter-Olesen and P. De-Camilli: Identification of the 64 k autoantigen in insulin-dependent diabetes as the GABA-synthesizing enzyme glutamic acid decarboxylase. Nature 347:151-156 (1990)], PA1 (4) cytoplasmic antigens [G. F. Bottazzo, A. Florin-Christensen, and D. Doniach: Islet Cell Antibodies in Diabetes Mellitus With Autoimmune Polyendocrine Deficiencies. Lancet 2:1279-1283 (1974), A. C. MacCuish, J. Jordan, C. J. Campbell, L. J. P. Duncan, and W. J. Irvine: Antibodies to Islet-Cell in Insulin-Dependent Diabetics With Coexistent Autoimmune Disease. Lancet 2:1529-1533 (1974), R. Lendrum, G. Walker, and D. R. Gambli: Islet-Cell Antibodies in Juvenile Diabetes Mellitus of Recent Onset. Lancet 1:880-883 (1975), and W. J. Irvine, C. J. McCallum, R. S. Gray, G. J. Campbell, L. J. P. Duncan, J. W. Farquhar, H. Vaughan, and P. J. Morris: Pancreatic Islet Cell Antibodies in Diabetes Mellitus Correlated With The Duration and Type of Diabetes, Co-existent Autoimmune Disease, and HLA-type. Diabetes 26:138-147 (1977)], PA1 (5) glycoconjugates [R. C. Nayak, M. A. K. Omar, A. Rabizadeh, S. Srikanta, and G. S. Eisenbarth, "Cytoplasmic" Islet Cell Antibodies: Evidence That the Target Antigen is a Sialoglycoconjugate. Diabetes 34:617-619 (1985); P. Vardi, E. E. Dibella, T. J. Pasquarello, and S. Srikanta, Islet Cell Autoantibodies: Pathobiology and Clinical Applications. Diabetes Care 10:645-56 (1987); B. K. Gillard, J. W. Thomas, L. J. Nell and D. M. Marcus, Antibodies Against Ganglioside GT3 in the Sera of Patients with Type I Diabetes Mellitus. Journal of Immunology 142:3826-32 (1989)].
Several reports indicate a high prevalence of anti-64 kd antibody in prediabetic sera as well as newly diagnosed diabetic sera [S. Baekkeskov, M. Landin, J. K. Kristensen, S. Srikanta, G. Jan Bruining, R. Mandrup-Poulsen, C. de Beaufort, J. S. Soeldner, G. Eisenbarth, F. Lindgren, G. Sundquist, and A. Lernmark: Antibodies to a 64,000 MW Human Islet Cell Antigen Precede the Clinical Onset of Insulin-dependent Diabetes. J. Clin. Invest. 79:926-934 (1987), M. A. Atkinson, N. K. Maclaren, W. J. Riley, D. W. Sharp and L. Holmes: Mr 64,000 Autoantibodies (64KA) Predict Insulin Dependent Diabetes. American Diabetes Assoc. 48th Annual Meeting (1988) Abstract #391, and M. A. Atkinson, N. K. Maclaren, D. W. Scharp, P. E. Lacy, and W. J. Riley: 64000 Mr autoantibodies as predictors of insulin-dependent diabetes. The Lancet 335:1357-1360 (1990)].
Some other molecular species have been characterized by Western blotting as being "common antigens" recognized by diabetic sera [D. G. Karounos, V. J. Virta, L. J. Nell, and J. W. Thomas: Analysis of Human and RINm5F Islet Cell Antigens. American Diabetes Assoc. Res. Symp. Woods Hole, Ma. October 1987; Abstract #120]. These antigens have molecular weights of 150 kd, 84 kd, 60 kd, 49 kd, and 36 kd. A more recent report from the same laboratory indicates that there is a RIN antigen of Mr 52,000 that reacts with 29% of diabetic sera. [D. G. Karounos and J. W. Thomas: Recognition of Common Islet Antigen by autoantibodies From NOD Mice and Humans With IDDM. Diabetes 39:1085-1090 (1990), D. G. Karounos, L. J. Nell, and J. W. Thomas: Autoantibodies present at onset of type I diabetes recognize multiple islet cell antigens. Autoimmunity 6:79-91 (1990), and D. G. Karounos, J. S. wolinsky, B. K. Gillard, and J. W. Thomas: Molecular Mimicry in Type I Diabetes: An Antigenic Determinant on a Rubella Virus Protein is Shared with a 52 kD Beta Cell autoantigen. Diabetes 39:96A (1990)]. The first and third references indicate that the 52,000 antigen is RIN specific, not found in human islets or other tissue.